Advanced Materials Research Vols. 160-162

Abstract: The reactions between Cu and the eutectic SnBi (Sn58wt.%Bi) solder alloy with and without 1wt.%Ni addition were investigated in this paper. After as-reflowed process, the IMCs formed in the Sn58wt.%Bi/Cu and Sn58wt.%Bi1wt.%Ni/Cu joints were Cu6Sn5 and (CuNi)6Sn5, respectively. During aging process, the thickness of the IMC layers formed at each solder/Cu joint increased, and a new layer Cu3Sn formed adjacent to the Cu substrate. It was found that 1wt.%Ni addition in Sn58wt.%Bi solder alloy could slightly enhance the growth rate of the total IMC layer, but effectively reduce the growth rate of Cu3Sn layer during aging process. The growth behavior of IMC layer for each joint followed the diffusion-controlled mechanism during aging.

Abstract: Chinese fir (Cunninghamia lanceolata Hook.) and Mongolian Scots pine (Pinus sylvestris Linn. var. mongolica Litv.) with dimension of 19.019.0450.0 mm were treated with two concentrations of amine copper quat-type D (ACQ-D) solutions (0.5%, 1.0%) respectively and post-treated with three different methods including humidity chamber, drying oven and hot water bath. The effects of these variables on copper leaching from ACQ-D treated wood were investigated according to the leaching test of AWPA E11. The results showed that post-treatment could improve the leaching resistance of ACQ-D treated wood effectively compared to the specimens those were leached immediately after impregnation. After some promising post-treatments, copper leaching from the treated wood was not only associated with the joint effects of retentions, wood species and different locations in the treated wood, but also influenced by the special fixation mechanisms in different post-treatments.

Abstract: Finite element simulation of stress distribution of thermal barrier coating system (TBCs) is presented. Two dimensional periodic unit cells are used to examine the stress development and critical sites with high potential of cracking during thermal cycling. During cooling, high tensile out-of-plane stresses in the peak of the thermally grown oxide (TGO) are formed, which lead to crack initiation in the vicinity of TGO and the interface. At the same time, high compressive stresses developed in the valley domain. The influence of crack within the top coat in the vicinity of the TGO is also investigated. The finite element analysis shows that crack seriously affects stress field development and the thermal-mechanical behavior of TBCs. Based on the finite element analysis results one can conclude that imperfections and its development should be always considered to be a crucial parameter for TBCs life.

Abstract: Since the nucleation of resistance spot welding is a close and invisible process, it is difficult to monitor its nucleation quality reliably. In order to estimate the quality of weld spot, this paper uses magnetic flux density around the nugget to reconstruct the current distribution in the faying surface between two workpiece. In the study, we found the inverse model of welding current and its magnetic flux density around the nugget. Since the model had ill-posedness, the regularization method was required to solve the problem. Conjugate Gradient Method was used to reconstruct the current distribution. The result shows that the image can reflect the main characteristic of current distribution, and it can be used for estimate the quality of weld spot.

Abstract: White light emitting polymers were synthesized through incorporating of low-band gap red light emitting 4,7-di(4-hexyl-thien-2-yl)-2,1,3-benzothiadiazole (DHTBT) moieties into the backbone of a blue-light-emitting poly(9,9-dioctylfluorene) (PFO). Incomplete energy transfer from the blue electroluminescent PFO backbone to the red light emitting unit occurred by carefully controlling the relative content of the low-band gap unit DHTBT in the resulting polymers. Pure white light electroluminescence from a single polymer has been obtained in a device with a configuration of ITO/PVK/polymer/Ba/Al.The highest external quantum efficiency is 1.04% at the luminance of 249 cd/m2 for the white emitting polymer with color coordinates (0.30, 0.35) very close to the CIE coordinates for National Television System Committee (NTSC) standard white-light emission (0.33,0.33).

Abstract: A simple and reliable welding method was developed to weld carbon nanotubes with the power supply here. The carbon nanotubes were synthesized chemical vapor deposition method and Multi-walled carbon nanotubes was uesd here. Firstly, apply less than 5 V voltages between carbon nanotubes when they were in close proximity under direct view of optical microscope. Then, let carbon nanotube contact with each other and increase the external voltage to 7–8V until carbon nanotube was attached to the end of the other, the two carbon nanotube join into a carbon nanotube. Furthermore, some experiments were implemented to analyze the reliability, the images of the weld joint and the weld strength all indicted this method were reliable.

Abstract: Due to the similarities between electrode model and their CNC machining process, process design could be finished efficiently using the electrode automatic classification system as well as the existed standard process template. This study developed an automatic classification retrieval system of electrode model by applying a statistical approach, namely SVM model, to the classification of electrode model, where 3D Polar-Radius Surface Moment was used to extract the feature vector of the electrode model. Experiments showed a promising result with an average classification accuracy up to 85.72% in addition to the high efficiency and usability. Most important, the developed approach is capable of reusing existing knowledge and experience and as a result it makes the CNC programming process easier.

Abstract: Rapid drawdown of water level is one of the most important factors that influencing the embankment stability. Based on the principle of geomechanical model test and hydroaulic model test methods, the model test was performed to study Yellow River downstream embankment instability induced by rapid drawdown of water level. The slope models with geometric scale of 1:25, 1:45, 1:62.5 were constructed in the transparent plexiglass model box with 1.6m long, 0.8m wide and 0.6m high. Changes on the slope were recorded during water level decline at different velocity by digital camera and slope tracer etc. The model test results showed that during the rapid drawdown process, there was only small cracks and not slippage in advance; when the water level dropped to a certain height, the sliding distance increased suddenly, which showed that the rate of water level decline was behind the river water, and the slope weight and downslope hydrodynamic pressure by the saturation line in slope body were higher than water lever exceeds the sliding force in a very short period of time, which caused landslide; after the sliding body appearing, slide was continuous and not mutation.

Abstract: Silica particles coated with PA12 by emulsion polymerization were used as fillers to reinforce PA12 based composites prepared by selective laser sintering (SLS). The influences of the treated and untreated particles on the sintering behavior and mechanical properties of the laser sintered specimens were investigated. It was found that there were many uneven holes in the untreated composites. However, for the treated composites, due to the silica particle surfaces treated by emulsion polymerization, the absorbance of laser was improved and the particles dispersed well in the polymer matrix; a full dense structure was obtained and the properties were enhanced, such as the tend strength increased 30%, the maximum value was 34MPa; the tensile strength increased up to 125%, the maximum value was 44.2 MPa, comparing to the unfilled PA12. Drawing from the results, it can be confirmed that a full dense structure can be obtained and the PA12 matrix was strengthened and toughened when the silica particles were coated with PA12 by emulsion polymerization.

Abstract: We have developed efficient pure white- and red-light-emitting polymers through incorporating of low-band gap orange-light-emitting 4-thienyl-2,1,3-benzothiadiazole (BTT) moieties into the backbone of a blue-light-emitting poly(9,9-dioctylfluorene) (PFO). Partial or complete energy transfer from the blue electroluminescent PFO backbone to the orange- light-emitting unit occurred by carefully controlling the relative content of the low-band gap unit BTT in the resulting polymers. Pure white- and red-light electroluminescence from a single polymer has been obtained in a device with a configuration of ITO/PEDOT:PSS/polymer/Ca/Al. The highest external quantum efficiency is 2.4% with luminous efficiency 2.20 cd/A at the luminance of 793 cd/m2 for the red-light emitting copolymer PFO-BTT with emission peak at 607 nm for 15mol% BTT content, the highest external quantum efficiency is 0.5% at the luminance of 81 cd/m2 for the white emitting polymer with color coordinates (0.34, 0.34) very close to the CIE coordinates for National Television System Committee (NTSC) standard white-light emission (0.33,0.33).